1. Field of the Invention
The present invention relates to methods of manufacturing surface acoustic wave apparatuses constructed by forming a plurality of surface acoustic wave devices having electrode films with different thicknesses on the same piezoelectric substrate, and, for example, relates to a method of manufacturing a surface acoustic wave apparatus in which a plurality of surface acoustic wave filter devices having different bands, are disposed on the piezoelectric substrate.
2. Description of the Related Art
Recently, in mobile communication apparatuses such as mobile phones, the apparatuses that support multi-band transmissions have been considered in order to achieve high-performance. In addition, the transmission frequencies of the mobile phones are getting higher.
Therefore, a mobile phone that can operate at an 800 MHz band as well as one having a 1.5 GHz or greater frequency band requires RF band-pass filters each corresponding to the two different frequency bands.
In order to achieve miniaturization and low overall weight of a terminal apparatus such as this type of a mobile phone, miniaturization of the components mounted therein must be achieved. However, since there is the limit as to how small the components can be, it is strongly desired that a single component perform the functions of the two RF band-pass filters.
In Japanese Unexamined Patent Application Publication No. 10-190390, there is disclosed a method of manufacturing a surface acoustic wave apparatus in which a plurality of surface acoustic wave filter devices are disposed on the same piezoelectric substrate.
FIGS. 10A to 10E are cross-sectional views illustrating the method of manufacturing the surface acoustic wave apparatus according to the above-described related art. In the method described in this related art, a conductive film 104 is formed on a piezoelectric substrate 103 and then a resist is formed along the entire surface of the conductive film 104. Patterning of the resist is performed to form a resist layer 105 (FIG. 10A). Dry etching forms electrodes 101a of a first surface acoustic wave device (FIG. 10B). Thereafter, deposition of the resist and patterning of the resist form a resist layer 106xe2x80x2 at a portion in which a second surface acoustic wave device is provided. In this case, a portion in which the first surface acoustic wave device is provided is coated with a resist layer 106 (FIG. 10C). Furthermore, as shown in FIGS. 10D and 10E, a conductive film 107 is entirely formed and then lift-off is performed on the resist layers 106 and 106xe2x80x2, and the conductive film 107 is laminated thereon to form electrodes 102a of the second surface acoustic wave device.
According to this method, in a state in which the electrodes of the first electric component device are protected by the resist, the electrodes of the second electric component device are formed by photolithography or etching. Accordingly, when the electrodes of the first and second electric component devices are formed, high accuracy is not required. Therefore, when this method is used for manufacturing a surface acoustic wave apparatus, even though the width of the electrode fingers are as fine as approximately 1 xcexcm, the efficiency percentage of manufacturing the apparatus can be increased.
However, in the method described in the related art, dry etching which is performed when the electrodes 101a of a first surface acoustic wave device are initially formed is also performed on a region where a second surface acoustic wave device is constructed on a piezoelectric substrate 103. That is, a region indicated by an arrow A in FIG. 10(b) is also subject to dry etching.
Generally, when dry etching is performed in a case in which an electrode finger pitch is approximately 1 xcexcm or less, due to a micro loading phenomena, a micro-gap portion is the last to be etched. In the dry etching, after etching is performed on the electrodes, generally over-etching follows.
Therefore, when the electrodes 101a of the first surface acoustic wave device are formed, etching is finished earlier in the region indicated by the arrow A. Accordingly, it takes a longer time for the surface of the piezoelectric substrate of the region indicated by the arrow A to be exposed to the plasma, such as F, which is used when dry etching including over-etching is performed. Since the surface of the substrate indicated by the arrow A is exposed to the plasma for the comparatively longer time, there is a problem that the insertion loss of the second surface acoustic wave device is degraded and VSWR is increased.
Furthermore, since the region indicated by the arrow A is also etched, the area of the etched region is increased. Accordingly, when a plurality of surface acoustic wave apparatuses is constructed from a mother piezoelectric substrate, there is a problem that a variation in the characteristic of the surface acoustic wave apparatus in the mother piezoelectric substrate increases.
In addition, when the manufacturing method according to the above-described related art is applied to a method of manufacturing the surface acoustic wave apparatus using a piezoelectric substrate having pyroelectricity, the following problem arises.
That is, generally, when the resist is deposited, the resist is often heated in order to improve adhesion and resistance to plasma of the resist pattern. However, when the piezoelectric substrate having the pyroelectricity is used, due to a temperature change during heating of the resist, a voltage drop occurs between a pair of comb-shaped electrodes which constitute the IDT electrodes of the first surface acoustic wave device, causing discharge. This discharge sometimes produces pyroelectric destruction in the electrodes. Even though discharge is too small to cause the pyroelectric destruction, the resist is sometimes broken, which causes a short circuit in the IDT electrodes of the first surface acoustic wave device after the lift-off process for constructing the electrodes of the surface acoustic wave device.
In order to overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing a surface acoustic wave apparatus which, even when a pyroelectric substrate is used in constructing a plurality of surface acoustic wave devices by forming electrodes having different thicknesses on the same piezoelectric substrate, short circuits or other defects are prevented from occurring, and degradation of the piezoelectric substrate is prevented from occurring in an electrode region of the subsequently formed surface acoustic wave device, and degradation of the insertion loss and degradation of the VSWR characteristics are prevented from occurring.
According to a first preferred embodiment of the present invention, a method of manufacturing a surface acoustic wave apparatus including first and second surface acoustic wave devices having different electrode film thicknesses on a piezoelectric substrate, the method including the steps of providing a piezoelectric substrate, forming a first conductive film on an entire surface of the piezoelectric substrate, depositing a first resist on the entire surface of the first conductive film, performing patterning and dry etching on the first resist to form on the piezoelectric substrate IDT electrodes of the first surface acoustic wave device, a short-circuit wiring electrode for establishing electrical connection between comb-shaped electrodes of the IDT electrodes, and a conductive film provided in a region including the entire area in which the second surface acoustic wave device is constructed, performing wet etching to remove the conductive film provided in the region including the entire area in which the second surface acoustic wave device is constructed, depositing a second resist on the entire surface of the piezoelectric substrate and heating the substrate, removing the second resist at a location in which the electrodes of the second surface acoustic wave device are located, forming a second conductive film having the same film thickness as the electrode film thickness of the second surface acoustic wave device, lifting off the second resist and the second conductive film deposited on the second resist, forming the electrodes of the second surface acoustic wave device while exposing the electrodes of the first surface acoustic wave device, and disconnecting the short-circuit wiring electrode in the first surface acoustic wave device.
A second preferred embodiment of the present application provides a method of manufacturing a surface acoustic wave apparatus including first and second surface acoustic wave devices having different electrode film thicknesses on a piezoelectric substrate, the method including the steps of providing a piezoelectric substrate, depositing a first resist on an entire surface of the piezoelectric substrate, removing the first resist at an area in which electrodes of the first surface acoustic wave device are to be formed and an area in which a wiring electrode for short-circuiting between the comb-shaped electrodes of the IDT electrodes of the first surface acoustic wave device is to be formed, forming a first conductive film having substantially the same film thickness as the electrode film thickness of the first surface acoustic wave device, lifting off the first resist and the first conductive film deposited on the first resist, forming the electrodes of the first surface acoustic wave device and the wiring electrode, depositing a second resist on the entire surface of the piezoelectric substrate and heating the substrate, removing the second resist at an area in which the electrodes of the second surface acoustic wave device are formed, depositing a second conductive film having substantially the same film thickness as the electrode film thickness of the second surface acoustic wave device, lifting off the second resist and the second conductive film deposited on the second resist, forming the electrodes of the second surface acoustic wave device, and disconnecting the short-circuit wiring electrode in the first surface acoustic wave device.
A third preferred embodiment of the present invention provides a method of manufacturing a surface acoustic wave apparatus including first and second surface acoustic wave devices having different electrode film thicknesses on a piezoelectric substrate, the method including the steps of providing a piezoelectric substrate, depositing a first resist on an entire surface of the piezoelectric substrate, removing the first resist at an area in which electrodes of the first and second surface acoustic wave devices are to be formed, forming a first conductive film having substantially the same film thickness as the electrode film thickness of the second surface acoustic wave device, depositing a second resist, removing the second resist at an area in which at least the electrodes of the first surface acoustic wave device are formed, except an area in which the second surface acoustic wave device is constructed, depositing a second conductive film having substantially the same film thickness as the electrode film thickness of the first surface acoustic wave device, and lifting off the first resist, the second resist, and the conductive films laminated thereon at the same time.
It is preferred that a negative-type resist is used as the first resist in the third preferred embodiment of the present invention.
In another modification of the third preferred embodiment of the present invention, a positive-type resist is preferably used as the first resist and the negative-type resist is used as the second resist. In the lift-off process, the separating liquid for separating the first and second resists is shared.
In manufacturing methods of surface acoustic wave apparatuses according to various preferred embodiments of present invention, when first and second surface acoustic wave devices having different electrode film thicknesses are formed on a common piezoelectric substrate, a short-circuit wiring electrode for electrically connecting between input/output terminals of the IDT electrodes and ground terminals is formed while the IDT electrodes of the first surface acoustic wave device are formed. After the IDT electrodes of the second surface acoustic wave filter device are formed, the short-circuit wiring electrode is disconnected. Hence, even though the second resist is deposited and adhesion and resistance to heat of the second resist are increased due to heating, the short circuit in the IDT electrodes of the first surface acoustic wave filter device is positively prevented.
Therefore, while malfunction of the IDT electrodes of the first surface acoustic wave filter device is prevented, the electrodes of the second surface acoustic wave filter can be highly accurately formed.
In the first preferred embodiment of the present invention, when dry etching is performed during formation of the IDT electrodes of the first surface acoustic wave filter device, a piezoelectric substrate portion in which the second surface acoustic wave filter device is formed is protected by the first resist. After the dry etching, a conductive film which is provided at a region including the portion in which the second surface acoustic wave device is formed is removed using a wet etching method. Accordingly, the region in which the second surface acoustic wave filter device of the piezoelectric substrate is formed can be prevented from being subjected to plasma such as F used in the dry etching. This enables the insertion loss and VSWR of the second surface acoustic wave filter device to be reliably and positively prevented from being degraded.
In manufacturing methods according to the second and third preferred embodiments of the present invention, when the first and second surface acoustic wave devices having different electrode film thicknesses are formed on the piezoelectric substrate, formation of the electrodes of the first surface acoustic wave filter device are performed using the lift-off method and the region in which the second surface acoustic wave filter device is formed is protected by the resist. Hence, compared with the conventional method in which the first surface acoustic wave filter device is formed using the dry etching method, degradation of the insertion loss and VSWR of the second surface acoustic wave filter device is reliably prevented.
Furthermore, according to the third preferred embodiment of the present invention, since there is no need to increase the accuracy during the second photolithography process, the heating temperature of the resist can be very low, which prevents the occurrence of pyroelectric destruction. Therefore, since formation of the short-circuit wiring electrode and a disconnection process are not required, simplification of the manufacturing processes can be achieved.
In addition, since the lift-off is simultaneously performed during the last process of which the electrodes of the first and second surface acoustic wave filter devices are formed, simplification of the processes can be achieved.
By causing the polarities of the first and second resists to be different, when patterning is performed on the second resist, deformation of the first resist can be prevented. This increases the electrode accuracy of the first surface acoustic wave filter device.
For the purpose of illustrating the present invention, there is shown in the drawings several forms that are presently preferred, it being understood, however, that the present invention is not limited to the precise arrangements and instrumentalities shown.
Other features, characteristics, elements and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.